Current commercial floral and horticultural foams are phenol/formaldehyde foams which are potential health hazards and have environmental problems because both phenol and formaldehyde are toxic chemicals subject to Section 313 of Title III of the Superfund Amendments and Reauthorization Act (SARA) of 1986 and 40 C.F.R. Part 372 reporting requirements. Also, formaldehyde is listed as a carcinogen by the National Toxicology Program (NTP), the International Agency for Research on Cancer (IARC), and the American Conference of Government Industrial Hygienists (ACGIH). Smithers-Oasis, U.S.A., and other companies currently market a phenol/formaldehyde foam ("PF foams"), and California presently requires the following label on PF foams: "Warning| This product contains a chemical known to the State of California to cause cancer."
Attempts have been made to provide nontoxic, environmentally friendly floral, agricultural, and horticultural foams, but to applicant's knowledge, none of these foams have been acceptable to the industry. One such unsuccessful attempt has been to develop silica foams by using the industry standard sodium silicate consisting of a water solution of sodium oxide (Na.sub.2 O) and silicon dioxide (SiO.sub.2) with the ratio of SiO.sub.2 to Na.sub.2 O at 3.22 and the soluble solids at 39.3 percent. This silica foam was produced in a continuous, high speed mixer by injecting a surface tension depressant (tall oil mix) and polymer forming agent (sodium fluorosilicate) into the sodium silicate. Also, cotton reinforcing fibers, such as cotton flock (260 microns) were mixed with sodium silicate to provide cohesive strength in the resulting foam, and coloring agents were added to provide the desired color. The final dry density of the foam was controlled by the injection of compressed air or nitrogen into the mixer. While this process and these raw materials produced a silica foam product with fine cells in the 40 to 60 microns diameter range, the best achievable liquid retention was at the 39 volume percent level due to capillary repulsion in the cellular structure. Another undesirable property of this foam was its hardness at the lowest practical density of near 4 pounds per cubic foot. When used as a floral foam for insertion of cut flowers, the hardness limited its use to large-stemmed flowers, and even then there was potential damage to the stems while inserting the flowers.
U.S. Pat. Nos. 3,741,898 and 3,856,539 produced silica foam products without the inclusion of any substantial amounts of fillers or reinforcements. By "substantial amounts" of fillers or reinforcements was stated to be an amount in excess of about 10 percent on a dry basis or about 3 percent by weight of the alkali metal silicate (commercial sodium silicate) raw material on a wet basis. These foam products were produced for use as structural and insulation materials but were never acceptable by the floral, agricultural, nursery, and horticulture industries.
The terms "silica" and "silicate" have been used interchangeably in the trade. In the foregoing patents, a silica foam product from sodium silicate solution is defined as not having over a substantial amount of filler (10 percent) of filler or reinforcement materials. In the present invention, considerably in excess of 10 percent "filler" and reinforcement material, such as activated carbon, and cellulosic fibers are present; and the caustic silicate solution derived from caustic digestion of rice hull ash has about 1/2 percent by weight of metals.
It would be highly desirable to provide a fine-celled, rigid foam composition which has improved absorption/adsorption and retention of liquids, which is not as hard as prior art foams so that, when used as a floral foam for insertion of cut flowers, hardness does not limit its use to large stem flowers and does not damage stems of the flowers while inserting them in the foam, which contains no harmful concentrations of polymerization by-products, such as sodium fluoride which is detrimental to cut flowers' life, does not require the addition of expensive coloring agents, and accordingly is desirable and suitable for floral uses.
It is also highly desirable to provide a foam composition suitable and useful as a propagation medium or blocks for plant and other agricultural cuttings, seeds, seedlings, nursery stock, trees, as soil conditioners, mulches, and the like.
It is also highly desirable to provide such a foam composition which is inexpensive, utilizes waste products, rice hull ash having diffused activated carbon throughout, and has valuable by-products acceptable to the various industries to which they pertain.